Human interleukin-18 (hIL-18) is a cytokine that is synthesized as a biologically inactive 193 amino acid precursor protein (Ushio, et al., J. Immunol. 156:4274, 1996). Cleavage of the precursor protein, for example by caspase-1 or caspase-4, liberates the 156 amino acid mature protein (Go, et al., Science 275:206, 1997; Ghayur, et al., Nature 386:619, 1997), which exhibits biological activities that include the costimulation of T cell proliferation, the enhancement of NK cell cytotoxicity, the induction of IFN-γ production by T cells and NK cells, and the potentiation of T helper type 1 (Th1) differentiation (Okamura, et al., Nature 378:88, 1995; Ushio, et al., J. Immunol. 156:4274, 1996; Micallef, et al., Eur. J. Immunol. 26:1647, 1996; Kohno, et al., J. Immunol. 158:1541, 1997; Zhang, et al., Infect. Immunol. 65:3594, 1997; Robinson, et al., Immunity 7:571, 1997). In addition, IL-18 is an efficacious inducer of human monocyte proinflammatory mediators, including IL-8, tumor necrosis factor-α (TNF-α), and prostaglandin E 2 (PGE 2) (Ushio, S., et al., J. Immunol. 156:4274-4279, 1996; Puren, A. J., et al., J. Clin. Invest. 10:711-721, 1997; Podolin, et al., J. Immunol. submitted, 1999).
The previously cloned IL-1 receptor-related protein (IL-1 Rrp) (Parnet, et al., J. Biol. Chem. 271:3967, 1996) was identified as a subunit of the IL-18 receptor (Kd=18 nM) (Torigoe, et al., J. Biol. Chem. 272:25737, 1997). A second subunit of the IL-18 receptor exhibits homology to the IL-1 receptor accessory protein, and has been termed AcPL (for accessory protein-like). Expression of both IL-1 Rrp and AcPL are required for IL-18-induced NF-κB and JNK activation (Born, et al., J. Biol. Chem. 273:29445, 1998). In addition to NF-κB and JNK, IL-18 signals through IL-1 receptor-associated kinase (IRAK), p56lck (LCK), and mitogen-activated protein kinase (MAPK) (Micallef, et al., Eur. J. Immunol. 26:1647, 1996; Matsumoto, et al., Biophys Biochem. Res. Comm. 234:454, 1997; Tsuji-Takayama, et al., Biochem. Biophys. Res. Comm. 237:126, 1997).
TH1 cells, which produce proinflammatory cytokines such as IFN-γ, IL-2 and TNF-β (Mosmann, et al., J. Immunol. 136:2348, 1986), have been implicated in mediating many autoimmune diseases, including multiple sclerosis (MS), rheumatoid arthritis (RA), type 1, or insulin dependent, diabetes (IDDM), inflammatory bowel disease (IBD), and psoriasis (Mosmann and Sad, Immunol. Today 17:138, 1996). Thus, antagonism of a TH1-promoting cytokine such as IL-18 would be expected to inhibit disease development. Il-18 specific mAbs could be used as an antagonist.
The role of IL-18 in the development of autoimmune diseases has been demonstrated. Accordingly, it has been demonstrated that IL-18 expression is significantly increased in the pancreas and spleen of the nonobese diabetic (NOD) mouse immediately prior to the onset of disease (Rothe, et al., J. Clin. Invest. 99:469, 1997). Similarly, IL-18 levels have been shown to be markedly elevated in the synovial fluid of rheumatoid arthritis patients (Kawashima, et al., Arthritis and Rheumatism 39:598, 1996). Furthermore, it has been demonstrated that IL-18 administration increases the clinical severity of murine experimental allergic encephalomyelitis (EAE), a Th1-mediated autoimmune disease that is a model for multiple sclerosis. In addition, it has been shown that neutralizing anti-rat IL-18 antiserum prevents the development of EAE in female Lewis rats (Wildbaum, et al., J. Immunol. 161:6368, 1998). Accordingly, IL-18 is a desirable target for the development of a novel therapeutic for autoimmunity.
Taniguchi, et al., J. Immunol. Methods 206:107, describe seven murine and six rat anti-human IL-18 monoclonal antibodies (mAbs), which bind to four distinct antigenic sites. One of the murine mAbs (#125-2H), and the six rat mAbs inhibit IL-18-induced IFN-γ production by KG-1 cells, with the rat mAbs exhibiting neutralizing activities 10-fold lower than that of #125-2H. As demonstrated by Western blot analysis, three of the murine mAbs, but none of the rat mAbs, are strongly reactive with membrane-bound human IL-18. In addition, an enzyme-linked immunosorbent assay (ELISA) to detect human IL-18 is described, utilizing #125-2H and a rat mAb. The limit of detection of this ELISA is 10 pg/ml.
European patent application EP 0 712 931 discloses two mouse anti-human IL-18 mAbs, H1 (IgG1) and H2 (IgM). As demonstrated by Western blot analysis, both mAbs react with membrane-bound human IL-18, but not with membrane-bound human IL-12. HI is utilized in an immunoaffinity chromatography protocol to purify human IL-18, and in an ELISA to measure human IL-18. H2 is utilized in a radioimmunoassay to measure human IL-18.
Neutralizing IL-18 antibodies may potentially be useful in relieving autoimmune diseases and related symptoms in man. Hence there is a need in the art for a high affinity IL-18 antagonist, such as a neutralizing monoclonal antibody to human interleukin 18, which would reduce Th1 cell differentiation and proliferation and thus autoimmune diseases and related symptoms.